Toilet tank valves function to admit water into a toilet tank after each flush discharge of stored water into the toilet. When the flush valve is closed, the tank valve remains open until the water level rises to a pre-established level. Then it closes, and barring leakage of either one of the valves, the pre-established volume of water remains in storage until the next flush cycle is initiated by opening the flush valve.
Requirements to reduce the volume of water needed for each flush cycle are becoming increasingly stringent. The decreasing availability of water for waste usage, and the overloading of sewer systems by unnecessarily large volumes of water used for a flush cycle, are only two of many reasons why governments are increasingly legislating limits on the types and demands of components of flush-type systems.
Of course the systems themselves include components other than the valves which are of importance. The shapes of the commode and of the tank are two such examples. The over-all objective is to obtain a flush with minimum water--perhaps only a gallon to a gallon and a half--which will clear the commode and provide just sufficient water to convey the waste material to the sewer and to refill the toilet boil.
Not surprisingly, various manufactures have taken different approaches to the problem. A sluggish flow, for example, is unlikely to clear all solid material in a single flush, and the toilet acts sluggishly and may not clear on one flush. For this reason, high velocity of the outlet stream is frequently sought and attained by appropriate design of the height of the maximum water level, and of the internal shape of the tank.
However, as to the manufacturer of the tank valve, the situation becomes more complicated. The "pottery" manufacturer simply wants to buy a lowest cost flush valve for any tank configuration he selects, and for any flushing scheme he may devise. To provide an individually manufactured valve to meet every wish of the customer is clearly impossible. In valves of this type, which should cost on the order of a dollar in view of the large numbers involved, the tooling must be commensurately expensive. Hard tooling cannot be changed to accommodate variations such as fractions of an inch in height, or of any other variable.
Especially for low volume emissions, height of the valve or relative height of the water level is one, but not always the most important parameter. Quick response, least impediment to water flow, freedom from silting up, and freedom from internal functional complications are a few others. As will further be discussed, below, the solution of one problem all to frequently creates a problem of it own.
What the industry requires is a standard, easily installed and serviced, quick-acting tank valve whose control function is very closely related to the water level, which is quickly and reliably activated when the water level departs from a pre-determined level and which holds its closed setting when the water level is at the pre-determined elevation, which enables a rapid flow of water, and whose operation occurs at a suitable rate that does not cause water hammer, or which causes the valve to hang up.
These simply-stated objectives are obvious enough, but many millions of dollars have been spent pursuing them with widely varying approaches to suitability for the intended purpose.